The present invention relates to extended light sources, and more specifically, to light sources having a region that appears to a viewer to be substantially uniformly lit such as, for example, a replacement for a neon tube or chemiluminescent light stick.
To minimize rear-end collisions, automobiles are currently equipped with an additional brake light, known as a center high mounted stop light (CHMSL), which is mounted in the rear windshield. This additional brake light is situated at a location that is likely to be in the line of sight of a driver in a vehicle immediately behind. The position of this brake light is therefore thought to be more effective at alerting the driver in the vehicle that the automobile in front is slowing down than is the traditional location of the brake lights adjacent the taillights.
The CHMSL brake light typically includes one or more incandescent light bulbs contained within a plastic opaque casing with one side of the casing comprising a red translucent plastic diffuser. When the brakes are activated, the incandescent bulbs are energized and light passes through the red diffuser thereby producing a red glow from the brake light. This red glow, however, is generally not very uniform. Since illumination is provided by incandescent bulbs situated behind the diffuser, regions on the diffuser near the bulbs are brightly lit, while regions farthest from the bulbs are more dim, creating variation in intensity across the brake light. Additionally, the diffusers typically comprise plastic sheets having surfaces contoured to distribute the light emitted from the bulbs. When the brake light is activated, these contours are brightly visible. As a result, the illumination provided is hardly uniform, as variation in the brightness across the brake light, as well as detail on the diffuser, are visible. This lack of uniformity detracts from the aesthetic appeal of these brake lights. Brake lights that produce a glow with irregularities and variation in intensity across the light seem to be less appealing than lights with a uniform intensity distribution. Essentially, a uniform glow appears cleaner and smoother, an effect that is highly desirable in lighting applications. Aesthetic appearance is extremely critical in marketing and sales of automobiles because consumers"" opinions of a vehicle are strongly influenced by its appearance. Consequently, car manufacturers are interested in improving the aesthetic appeal of their vehicles. If uniformly lit brake lights are aesthetically pleasing, then they will be more marketable. Thus what is needed is a light source having an extended region that appears to the viewer to be substantially uniformly lit.
In one aspect of the invention, an illumination apparatus comprises an elongated waveguide having proximal and distal ends and a central longitudinal axis. The waveguide comprises an elongated forward side for outputting light and an elongated rearward side for reflecting light towards the forward side. The rearward side includes an elongated reflective surface. A solid state light emitter is on the proximal end of the waveguide and introduces light into the waveguide in the form of a substantially collimated beam having a divergence angle xcex1. The waveguide has a width at the distal end that is approximately equal to 2 L tan(xcex1), where L is the length of the waveguide between the ends.
Another aspect of the invention also comprises an illumination apparatus comprising an elongated waveguide having proximal and distal ends and a central longitudinal axis. In addition, the waveguide comprises an elongated forward side for outputting light and an elongated rearward side for reflecting light towards the forward side. The rearward side includes an elongated reflective surface. A solid state light emitter is on the proximal end of the waveguide and introduces light into the waveguide. The distal end of the waveguide has a reflective surface which is non-perpendicular to the central axis of the waveguide.
Yet another aspect of the invention comprises an illumination apparatus comprising an elongate waveguide with a forward side for outputting light and a rearward side for reflecting light toward the forward side. The waveguide comprises first and second waveguide portions, each of the portions comprising an elongate concave transmissive output surface and an elongate reflective surface. The elongate waveguide portions are joined such that (i) the transmissive surfaces are in side-by-side relationship and such that (ii) the elongate reflective surfaces converge towards the forward side and flare outwardly toward the rearward side.
In still another aspect of the invention, an illumination apparatus comprising an elongated waveguide comprising an elongated forward side having a concave surface for outputting light and an elongated rearward side having a convex surface for reflecting light towards the forward side. The convex surface of the rearward side comprises an elongated reflective surface.
In yet another aspect of the invention, an illumination apparatus comprises an elongated waveguide comprising an elongated forward side for outputting light and an elongated rearward side for reflecting light towards the forward side; the rearward side comprises an elongated reflective surface. A non-imaging optical element on one end of the waveguide couples light from a light source into the waveguide. The non-imaging optical element provides an input aperture and an output aperture, wherein one of the apertures is larger than the other. The non-imaging optical element has sidewalls curved longitudinally between the input and output apertures such that the sidewalls couple light from the input aperture to the output aperture.
In still another aspect of the invention, an illumination apparatus comprises an elongated waveguide having a central longitudinal axis and a cross-section perpendicular to the longitudinal axis. The waveguide includes an elongated forward side having an elongate illumination surface for outputting light and an elongated rearward side for reflecting light towards the forward side. The rearward side comprises an elongated reflective surface. The waveguide is cross-sectionally shaped to function as a non-imaging optic for light propagating from the rearward side to the forward side.